Certain devices such as wafer defect scanners, laser printers, augmented reality devices, document scanners, projectors and the like often employ a collimated laser beam that scans across a surface in a straight or curved line path. These devices employ tilting mirrors to deflect the beam to perform the scanning. These tilting mirrors may be, or may include, Micro Electro Mechanical Systems (“MEMS”) devices. The actuation of mirrors used in MEMS devices, referred to herein as MEMS mirrors, can be via the electromagnetic, electrostatic, piezoelectric, and thermoelectric effects, depending on application.
One type of common MEMS mirror includes a stator and a rotor, with the rotor or structures carried by the rotor being reflective. The stator and/or rotor are driven with a drive signal which results in the rotor oscillating with respect to the stator, thereby changing the angle of reflectance of an incident light beam on the rotor. By oscillating the rotor between two orientations, an opening angle of the mirror is defined, and scanning of the light beam across the surface is accomplished.
Precise control of the opening angle of the mirror is desirable for the precise application in which such mirrors are used. When there is a non-constant phase difference between the drive signal and the angle of the rotor, it can be difficult to synchronize the MEMS mirror with the light beam to clearly project images onto a surface. Video standards, especially high definition video standards use hundreds of bits per scan line, hence the significance in the accuracy of the precise control of the mirror's position and the synchronization with the light beam.
So as to provide this precise control, development in the area of the detection of such phase differences, and in the control of such phase differences to maintain them as desired, is needed.